Mailchannel.net appears to have arisen as a popular email delivery
service. It is also somewhat broken. For no obvious reason it bounces
the message back and forth between the itself and the originating
sender at least 10 times before actually sending the message on to its
recipient.
The result is a huge header with a larger number of "Received: ..."
and "X-whatever" header entries. CGPro has been rejecting some of
these messages because of the large number of Received entries.